Ann Nucl Med (2014) 28:551–558
DOI 10.1007/s12149-014-0845-6

ORIGINAL ARTICLE

Application of a medium-energy collimator for I-131 imaging
after ablation treatment of differentiated thyroid cancer
Masato Kobayashi • Hiroshi Wakabayashi • Daiki Kayano • Takahiro Konishi •Hironori Kojima • Hiroto Yoneyama • Koichi Okuda • Hiroyuki Tsushima •Masahisa Onoguchi • Keiichi Kawai • Seigo Kinuya

Received: 9 February 2014 / Accepted: 19 March 2014 / Published online: 8 April 2014
Ó The Japanese Society of Nuclear Medicine 2014

Abstract
Purpose High-energy (HE) collimators are usuallyapplied for I-131 imaging after ablation treatment of differentiated thyroid cancer (DTC). However, purchase of
HE collimators has been avoided in many nuclear medicine
departments because the HE collimators are more expensive than other collimators. In this study, we compared theI-131 imaging using HE- and medium-energy (ME) collimators, which is more versatile than HE collimators.
Materials and methods To simulate DTC patients withextra-thyroid beds, a phantom of acrylic containers containing I-131 was used. To simulate patients with thyroid
beds, four phantoms representing extra-thyroid beds werearranged around the phantom representing normal thyroid
tissues. Patients administered 1.11 or 3.70 GBq NaI-131
were also evaluated. Whole-body imaging and SPECT
imaging of the phantoms and patients performed using HEgeneral-purpose (HEGP) and ME-low-penetration (MELP)

M. Kobayashi (&)  M. Onoguchi  K. Kawai
School of Health Sciences, College of Medical, Pharmaceuticaland Health Sciences, Kanazawa University, 5-11-80 Kodatsuno,
Kanazawa 920-0942, Japane-mail: kobayasi@mhs.mp.kanazawa-u.ac.jp
H. Wakabayashi  D. Kayano  K. Okuda  S. Kinuya
Department of Biotracer Medicine, Kanazawa University
Graduate School of Medical Sciences, Kanazawa, JapanT. Konishi  H. Kojima  H. Yoneyama
Department of Radiology, Kanazawa University Hospital,
Kanazawa, Japan
H. Tsushima
Department of Radiological Sciences, Ibaraki Prefectural
University of Health Sciences, Ibaraki, Japan

collimators, and full-width at half maximum (FWHM) andpercent coefficient of variation (%CV) were measured.
Results In the extra-thyroid beds, FWHM and %CV with
MELP were negligibly different from those with HEGP in
whole-body imaging. Although FWHM with MELP was alittle different from that with HEGP in SPECT imaging, %CV with MELP was significantly higher than thatwith HEGP. In the thyroid beds, only an extra-thyroid bed
including higher radioactivity was identified in whole-body
imaging with both collimators. Although SPECT images
with MELP could not clarify extra-thyroid beds with low
radioactivity, HEGP could identify them. In patients,
although some whole-body images with MELP could notdetect extra-thyroid beds, whole-body imaging with HEGP
and SPECT imaging with both collimators could detect
them.
Conclusions Although HEGP is the best collimator for
I-131 imaging, MELP is applicable for not only wholebody imaging but also SPECT imaging.
Keywords NaI-131  Ablation  Differentiated thyroid
cancer  Medium-energy collimator  High-energy
collimator

Introduction
A capsule including radioactive sodium iodine-131 (NaI131) is administered orally for ablation treatment of differentiated thyroid cancer (DTC) [1–3]. Ablation treatment
with I-131 [1.11 GBq (30 mCi) is often performed on an
inpatient basis, whereas treatment with I-131 B1.11 GBq isoften done on an outpatient basis [4, 5].
I-131 imaging with whole-body and SPECT scanning isa useful tool for identifying the location of DTC or

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metastases and evaluating the effect of the treatment [6–8].
Selection of the appropriate collimator is important toobtain clear images in nuclear medicine imaging. In general, high-energy (HE) and medium-energy (ME) collimators are used for energy range of 300–500 and
150–300 keV, respectively. Although HE collimators are
ideally applied for I-131 imaging because of the highphoton energy of I-131 [9, 10], the HE collimators are
more expensive than that of other collimators and thepurchase of HE collimators has been avoided for many
nuclear medicine departments in hospital. In this case,medium-energy (ME) collimators have been used for I-131
imaging [11, 12]. However, the suitability of ME collimators for I-131 imaging has not been extensively evaluated. In this study, we compared I-131 imaging after
ablation treatment of DTC using ME and HE collimators.
The image quality was evaluated using phantoms to simulate a single extra-thyroid bed and thyroid beds containing
cancer, as in patients with DTC. The I-131 radioactivity
was estimated as 1.11 GBq for outpatients and 3.70 GBq(100 mCi) for inpatients.

Materials and methods
Point source and phantoms
Performance tests with ME-low-penetration (MELP) andHE-general-purpose (HEGP) collimators were performed
to measure the system resolution and sensitivity in planar
imaging at 10 cm from a 37 MBq (1 mCi) I-131 point
source.
Image and size of phantom and schematic layout for
simulation of thyroid beds are also shown in Fig. 1. An
acrylic cylindrical container (20 mm in diameter and
10 mm thick, with a 5-mm diameter cylindrical hole) wasused as a phantom to simulate uptake of extra-thyroid beds
and thyroid beds after thyroidectomy (Fig. 1a, b). To
simulate the extra-thyroid beds including lymph nodemetastases, the phantoms containing 1.85 MBq (50 lCi)
I-131 were placed in the center of the field of view (FOV)in the images.
To simulate thyroid beds, four phantoms containing 5.55
or 18.5 MBq (0.15 or 0.5 mCi) were placed in the center of
the FOV, and four phantoms including 0.19, 0.37, 0.74 or
1.85 MBq (5, 10, 20 or 50 lCi) were set up around the four
phantoms representing normal thyroid tissues to simulate
extra-thyroid beds (Fig. 1c). These containers were placedon an acrylic board, which simulated the body of a patient.
The acrylic board was placed on the table for patients in the
SPECT scanner (Fig. 1d). The I-131 radioactivity wasdetermined by measuring the radiation exposure of patientsusing the medical internal radiation dose (MIRD) method

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a

b

5 mm
5 mm
10 mm

20 mm

c

d
1.85 MBq

0.37 MBq

0.19 MBq

30 mm
0.74 MBq
30 mm

5.55, 18.5 MBq
1.85 MBq

0.37 MBq

0.74 MBq

0.19 MBq

Fig. 1 Image and size of phantom and schematic layout were shownas simulation of thyroid beds. Image of phantom simulating single
extra-thyroid beds and thyroid beds (a); size of phantom (b);schematic layout of thyroid beds (c); and phantom set-up (solid
arrow) on patient bed (d). In the thyroid beds, four phantoms
containing 5.55 or 18.5 MBq of I-131 simulated normal thyroid
tissues and four phantoms including 0.19, 0.37, 0.74 or 1.85 MBq of
I-131 were placed around these phantoms to simulate extra-thyroid
beds

at 3 days after oral administration of 1.11 or 3.70 GBq
NaI-131 for ablation.
SPECT/CT camera
The SPECT scanner was equipped with a dual-headgamma camera with 9.5-mm-thick NaI crystals, had a38.7 9 53.3 cm FOV, and was combined with a spiral6-slice CT (80, 110 and 130 kV, 20–345 mA, and 0.8, 1.0
and 1.5 s rotation time) in the same gantry (SymbiaT6;
Siemens Medical Solutions, Erlangen, Germany) [14].
HEGP and MELP collimators were selected for the I-131
imaging study. The specifications of the HEGP and MELP
collimators are presented in Table 1.
Whole-body and SPECT image acquisition in phantoms
Whole-body and SPECT acquisition methods with NaI-131
for the ablation were established in our previous study [13].
For whole-body imaging, each collimator was 10 cm fromthe phantom. Images were acquired at table speeds of 10,
15 or 20 cm/min using a 256 9 1024 matrix (2.4-mm pixel

Ann Nucl Med (2014) 28:551–558

553

Table 1 Collimator specifications of MELP and HEGPCollimator
Isotope

MELP
Ga-67

HEGP
I-131

Hole shape

Hexagonal

Hexagonal

Table 2 FWHM and %CV of the whole-body imaging with I-131 of
1.85 MBq
Table speed (cm/min)

FWHM (mm)

%CV

MELP

HEGP

MELP

HEGP

Number of holes (91000)

14

8

10

15.9

15.5

28.2

27.6

Hole length (mm)

40.64

50.80

15

16.1

15.8

30.0

29.6

Septal thickness (mm)

1.14

2.00

20

16.2

16.2

39.4*

38.6

Hole diameter (mm across the flats)

2.94

3.40

Sensitivity at 10 cm (cpm/kBq)

8.38

3.84

System resolution at 10 cm (mm)Septal penetration (%)

12.5
1.2

14.6
3.5

* P \ 0.05 vs. HEGPsize) and a 364-keV photopeak with a 15 % window.
SPECT images were scanned using step and shoot with 60
projections (6 degrees/projection) for 360-degree acquisition at 20 s per projection. Image matrix sizes and the scanenergy window were a 256 9 256 matrix and zoom 1 (2.4mm pixel size), a 128 9 128 matrix and zoom 1 (4.8-mm
pixel size) and a 364-keV photopeak with a 15 % window.
After SPECT scans, CT transmission scans were performed
at 130 kV with a rotation time of 0.6 s. The slice thicknessof CT images was set at 4.8 mm (default image slice).

dimensional (3D) (OSEM-3D) algorithm, called Flash
3DTM in Siemens Medical Solutions [15]. The OSEM-3D
algorithm included depth-dependent detector responsemodeling resolution recovery, attenuation correction,
scatter correction and a Gaussian post-filter with twofold
full-width at half maximum (FWHM) of pixel size. In the
OSEM-3D algorithm, subset and iteration were, respectively, set up to 12 and 10 because the combination ofsubset and iteration improved recovery coefficients compared with other combinations [15]. In addition, scattercorrection was not applied to the phantom study because
there was no background activity.

Whole-body and SPECT scans in patients

Imaging and statistical analysis

Two female patients, 46 and 54 years old, with thyroglobulin (Tg) level (\5 and 482 ng/mL, respectively) wereadministered 1.11 GBq I-131, and two male patients, 58
and 73 years old, with Tg level (282 and 157 ng/mL,
respectively) were administered 3.70 GBq I-131. Wholebody and SPECT images of NaI-131 at a therapeutic
radioactive dose of 1.11 or 3.70 GBq were acquired at
3 days after NaI-131 administration. The study wasapproved by the ethics committee of our hospital. Written
informed consent was obtained from each subject. From theresults of a previous study [13], whole-body scans were
performed using a table speed of 15 cm/min, and SPECT
scans were obtained using step-and-shoot with 60 projections (6 degrees/projection) for 360-degree acquisition at
20 s per projection. The image matrix size and scan energy
window were a 128 9 128 matrix and zoom 1 (4.8-mm
pixel size) and a 364 keV photopeak with a 15 % window
and 15 % sub-window for scatter correction with triple
energy window. Attenuation correction was performed
using CT. In patients, SPECT and CT images were obtained
covering areas of the cervical region/thyroid bed and suspected abnormal accumulation on whole-body images.

An approximately 5-mm region of interest (ROI) was
located in the center of the phantom. The ROI was thesame size as the hole in the phantoms. The resolution wasmeasured by FWHM (mm), and image noise was definedas the coefficient of variation (%CV, standard deviation/mean 9 100 (%)) of pixel values within an ROI. Image J
was applied to obtain profile curves on SPECT images withboth collimators [16]. A statistical software package(JMPÒ version 9 SAS Institute Inc., Cary, NC, USA) wasused for statistical analysis using a paired t test. Statistically significant differences were defined as P \ 0.01 or
0.05.

Reconstruction of SPECT data
SPECT data were reconstructed using ordered subsets
expectation maximization (OSEM) with a three-

Results
System resolution and sensitivity using MELP were,respectively, 14.8 mm and 9.82 cpm/kBq at 10 cm fromthe I-131 point source, whereas HEGP showed 14.6 mm
and 3.84 cpm/kBq.
For the simulation of the extra-thyroid beds, FWHM
and %CV on whole-body images using 1.85 MBq I-131
are shown in Table 2. Although FWHM and %CV with
MELP were negligibly different from those with HEGP at
all table scan speeds, the %CV showed a significantly highvalue at a table speed of 20 cm/min (P \ 0.05). Table 3
shows FWHM on the SPECT imaging with different pixel

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Table 3 FWHM of the SPECT
imaging with different pixel
sizes and I-131 radioactivity

FWHM (mm)Radioactivity (MBq)

0.19

Pixel size (mm)

MELP

HEGP

MELP

HEGP

MELP

HEGP

MELP

HEGP

2.4

11.5

11.3

11.3

10.9

11.0

10.8

10.9

10.6

4.8

12.6

12.4

12.6

12.2

12.6

12.1

12.3

12.2

a

0.37

b

0.74

1.85

c
4000

Counts1.85 MBq

MELP

3000

0.37 MBq

0.19 MBq

2000
1000

0.74 MBq
0

Counts2400

HEGP
Table speed(cm/min)

10

15

20

1600
800
0

Fig. 2 Whole-body images (a), profile curves (b) and schematiclayout (c) were showed using simulated thyroid beds estimating
patients administered 1.11 GBq of I-131. On schematic layout,
vertical line was located to obtain profile curves. In profile curves andthe images with both collimators, although only the extra-thyroid beds

including 1.85 MBq were distinguished from phantoms simulating
normal thyroid tissues at all table speeds of 10 (dashed line), 15 (solidline) and 20 cm/min (dotted line), other extra-thyroid beds were notconfirmed because MELP yielded more radioactive scatter thanHEGP

sizes and I-131 radioactivity. There were no significant
differences in FWHM between MELP and HEGP at pixel
sizes of 2.4 and 4.8 mm. However, %CV of MELP was
significantly higher than that of HEGP (P \ 0.01).
In the simulation of the thyroid beds of DTC patientsadministered 1.11 GBq I-131, only the 1.85 MBq phantom
simulating an extra-thyroid bed was differentiated fromphantoms simulating normal thyroid tissues on the wholebody imaging using both MELP and HEGP (Fig. 2). On theother hand, SPECT images with HEGP identified the0.19 MBq phantom, whereas MELP could not identify the0.19 and 0.37 MBq phantoms (Fig. 3). These results
showed the same tendency with the simulation of the
thyroid beds for estimating patients administered 3.70 GBq
I-131 (data not shown).
Whole-body and SPECT images of two patients administered 1.11 GBq are shown in Figs. 4 and 5. In a patientwith low uptake of I-131 in the thyroid beds (Fig. 4), I-131
thyroid uptake with MELP in the whole-body imaging(Fig. 4a) was much lower than that with HEGP and SPECT
imaging with both collimators (Fig. 4b–d). In whole-body
images of another patient with high uptake of I-131 in the
thyroid beds, extra-thyroid beds could not be detected using

MELP (Fig. 5a), but could be detected using HEGP
(Fig. 5c). On the other hand, SPECT images could differentiate extra-thyroid beds and thyroid beds using both collimators (Fig. 5b, d).
Whole-body and SPECT images of two patientsadministered 3.70 GBq are shown in Figs. 6 and 7. In apatient with lower uptake of I-131 in the thyroid beds,
although whole-body images with MELP could not detect
the thyroid beds, whole-body imaging with HEGP and
SPECT imaging with both collimators could detect the
thyroid beds (Fig. 6). In whole-body images of another
patient with high uptake of I-131 into the thyroid beds,
whole-body and SPECT images using both collimators
could differentiate the thyroid beds (Fig. 7).

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Discussion
I-131 imaging is necessary to confirm the efficacy ofablation treatment because treatment and care for patientswith thyroid beds and/or lymph node metastases differ
from those for patients without thyroid beds and/or lymph
node metastases [10, 17]. Although selecting theAnn Nucl Med (2014) 28:551–558

555

b

1200

Counts

a

MELP

c

900
600
300
0

Counts

600

HEGP

Pixel size
(mm)

2.4

4.8

400
200
0

Fig. 3 SPECT images (a), profile curves (b) and schematic layout(c) were shown using simulated thyroid beds estimating patientsadministered 1.11 GBq of I-131. On schematic layout, horizontal line
was located to obtain profile curves. In the profile curves, dashed line
showed the results of SPECT scan with 2.4-mm pixel size and solidline showed those of SPECT scan with 4.8-mm pixel size. In the
SPECT images with HEGP were able to differentiate the thyroid beds
including 0.19 and 0.37 MBq from phantoms simulating normal
thyroid tissues compared to those with MELP, although the effect ofpixel size was small

Fig. 4 Thyroid beds in a 46-year-old female patient after ablation
treatment with 1.11 GBq I-131. There was lower uptake of I-131 inthyroid beds in patients administered 1.10 GBq. a A whole-body
image with MELP showed low uptake in the thyroid beds (solid
arrow). On the other hand, b a SPECT image with MELP, c a wholebody image with HEGP, and d a SPECT image with HEGP showed

higher uptake in the thyroid beds compared to a whole-body image
with MELP (solid arrow). The serum stimulated thyroglobulin levelat I-131 ablation was \5 ng/mL. Although whole-body images with
MELP could not detect the thyroid beds, whole-body imaging withHEGP and SPECT imaging with both collimators could detect the
thyroid beds

Fig. 5 A 54-year-old female patient with extra-thyroid beds after
ablation treatment with 1.11 GBq I-131. There was higher uptake of
I-131 in thyroid beds in patients administered 1.10 GBq. a A wholebody image with MELP caused many star artifacts (solid arrow). On
the other hand, b a SPECT image with MELP, c a whole-body image
with HEGP, and d a SPECT image with HEGP identified thyroid beds

(solid arrow) and extra-thyroid beds (broken arrow). The serum
stimulated thyroglobulin level at I-131 ablation was 482 ng/mL.
Extra-thyroid beds could not be detected using MELP, but could be
detected using HEGP. SPECT images could differentiate extrathyroid beds and thyroid beds using both collimators

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Fig. 6 Thyroid beds in a 58-year-old male patient after ablation
treatment with 3.70 GBq I-131. There was lower uptake of I-131 in
the thyroid beds in patients administered 3.70 GBq. a A whole-body
image with MELP showed a large star artifact (solid arrow). b A
SPECT image with MELP, c a whole-body image with HEGP, andd a SPECT image with HEGP identified thyroid beds (solid arrow)and extra-thyroid beds (broken arrow). The serum stimulated
thyroglobulin level at I-131 ablation was 282 ng/mL. Althoughwhole-body images with MELP could not detect the thyroid beds,
whole-body imaging with HEGP and SPECT imaging with bothcollimators could detect the thyroid beds

Fig. 7 A 73-year-old male patient with extra-thyroid beds after
ablation treatment with 3.70 GBq I-131. There was higher uptake of
I-131 in thyroid beds in patients administered 3.70 GBq. a A wholebody image with MELP, b a SPECT image with MELP, c a wholebody image with HEGP, and d a SPECT image with HEGP

differentiated the thyroid beds (solid arrow). The serum stimulated
thyroglobulin level at I-131 ablation was 157 ng/mL. In this case,whole-body and SPECT images using both collimators could
differentiate the thyroid beds

appropriate collimator is important to obtain clear I-131
images, the costs of the collimators are important for many
hospitals. Especially, HE collimators are not economical
because they can only be applied for I-131 (mainly
364 keV) imaging. ME collimators are usually applicablefor gallium-67 (mainly 93 and 184 keV), indium-111 (171and 245 keV), indine-123 (mainly 159 keV) imaging, etc.
Although the yields of ME collimators can be estimated,
ME collimators have more star artifacts than HE collimators because ME collimators are thinner and have more
septal penetration. ME collimators are, however, moreversatile than HE collimators. In this study, MELP wasapplied for I-131 imaging after ablation treatment of DTC.
The system resolution and sensitivity of the camera withHEGP were respectively 14.6 mm and 3.84 cpm/kBq at
10 cm from the I-131 source, whereas those with MELP
were respectively 14.8 mm and 9.82 cpm/kBq. There wasa negligible difference in system resolution between HEGP
and MELP, and sensitivity with MELP was higher thanthat with HEGP because of the septal penetration andradioactive scatter of MELP. Tan et al. [18] reported thatthe image contrast of I-131-Tositumomab with an HE
collimator was greater than that with an ME collimator inwhole-body imaging. In addition, the sensitivity of an ME
collimator was approximately 2.8-fold higher than that ofan HE collimator. Our results with planar imaging weresimilar to Tan’s results with whole-body imaging.
In the simulation of the extra-thyroid beds on wholebody imaging, FWHM with MELP was slightly worse thanthat with HEGP at all table scan speeds. The %CV of
MELP was significantly higher than that of HEGP at atable speed of 20 cm/min because there is a lot of noise in
I-131 imaging with MELP at this table speed (Table 2).
Tan et al. [18] showed the image contrast at a table speedof 20 cm/min was not significantly different from that at atable speed of 100 cm/min; however, image noise
increased with the lower counts at 20 cm/min comparedwith 100 cm/min. Mah et al. [19] reported that there is no
significant difference in I-131 half-life and residence timemeasurements using the same table speed in whole-body123

Ann Nucl Med (2014) 28:551–558
Table 4 %CV of the SPECT
imaging with different pixel
sizes and I-131 radioactivity** P \ 0.01 vs. HEGP

557

FWHM (mm)Radioactivity (MBq)

0.19

Pixel size (mm)

MELP

HEGP

MELP

HEGP

MELP

HEGP

MELP

HEGP

2.4

16.2**

14.2

16.1**

14.0

15.3**

13.9

15.2**

13.5

4.8

25.7**

20.0

25.1**

20.3

24.9**

20.5

25.2**

20.3

imaging with HEGP and MELP. Therefore, FWHM andimage contrast will not be different between HEGP and
MELP in spite of different table speeds in whole-body
imaging. Image noise, however, will slightly increase when
MELP is applied for whole-body imaging at faster tablespeeds. In SPECT imaging with different pixel sizes andradioactivity, although FWHM of MELP was a little different from that of HEGP (Table 3), %CV of MELP was
significantly higher than that of HEGP (Table 4). Basically, the FWHM of SPECT resolution is independent of
the low radioactivity level using filtered back projection ofreconstruction algorithm. In our study, OSEM-3D yieldedslightly higher SPECT resolution and lower %CV whenradioactivity in the phantom was gradually increased from
0.19 to 1.85 MBq. In addition, the OSEM-3D with MELP
showed a smaller effect than that with HEGP.
In the simulation of the thyroid beds, the radioactivity ofthe thyroid beds was appropriate because radioactivity wasdetermined by measurement in the thyroid area of patientswith DTC administered 1.11 or 3.70 GBq I-131 using the
MIRD method. Only 1.85 MBq phantoms could be distinguished from normal thyroid beds using both collimators
in whole-body imaging (Fig. 2). However, MELP yielded
more star artifacts than HEGP. SPECT images with MELP
could not identify the phantom with low radioactivity of
0.19 and 0.37 MBq because MELP also produced a lot ofradioactive scatter and star artifacts, and the phantom withlow radioactivity was not different from backgroundradioactivity in the SPECT imaging. HEGP identified thephantom with low radioactivity using OSEM-3D with theresolution correction method (Fig. 3). Koral et al. [20]showed the usefulness of OSEM-3D using a whole-bodyphantom including I-131 and an HE collimator. When there
is a low I-131 radioactivity in the thyroid beds, the effect ofresolution correction in the OSEM-3D will be small
because radioactivity of the thyroid beds cannot be differentiated from background radioactivity.
Because these simulation studies using phantoms were
performed without background radioactivity, we also performed clinical studies with background radioactivity. In
patients administered 1.11 GBq I-131, lower uptake of
I-131 in the thyroid beds could not be detected using
whole-body imaging with MELP because the uptake wasburied in the noise of background radioactivity (Fig. 4a).

0.37

0.74

1.85

However, the uptake was detected using whole-body
imaging with HEGP and SPECT imaging with both collimators (Fig. 4b–d). This is because HEGP has lower septal
penetration than MELP, and use of OSEM-3D and a resolution correction method with SPECT imaging reduced
the image noise and improved image contrast. In another
patient administered 1.11 GBq I-131, there was extensive
I-131 uptake in the thyroid beds compared with the other
patient, as shown in the Fig. 4. Although we could notdetect extra-thyroid beds in the whole-body imaging with
MELP because of star artifacts, whole-body imaging withHEGP decreased the amount of star artifacts and was able
to detect the extra-thyroid beds (Fig. 5a, c). On the other
hand, SPECT images with both collimators could differentiate the thyroid beds (Fig. 5b, d). In the United States,
some European countries and Japan, I-131 at B1.11 GBq issufficient for ablation treatment of patients with DTC as
outpatients [5, 21–23]. In addition, to maximize costeffectiveness such as application of MELP, some hospitals
that can perform I-131 ablation do not have an HE collimator and inpatient facility. In that case, it will be useful toperform I-131 ablation imaging with ME collimators as an
outpatient treatment.
In two patients administered 3.70 GBq I-131, wholebody images with MELP could not identify thyroid beds in
one patient with DTC exhibiting low uptake of I-131 inthyroid beds because of the presence of many star artifacts(Fig. 6a), whereas whole-body imaging with HEGP and
SPECT imaging with both collimators were able to differentiate the thyroid beds (Fig. 6b–d). OSEM-3D, which
decreased image noise and increased image contrast, had asignificant effect on the SPECT imaging. In thyroid beds
with higher uptake of I-131, there were no differences inwhole-body and SPECT imaging between the collimators,
although MELP also yielded star artifacts. In this patient,
there was extensive thyroid uptake of I-131 compared withbackground radioactivity and star artifacts. In this case,although SPECT imaging may not be necessary in MELP,
the increased uptake may be caused by star artifacts
merging with regions of I-131 uptake representing thyroid
cancer and/or lymph node metastases. Therefore, whenselecting MELP in the whole-body imaging of ablation
treatment using 1.11 and 3.70 GBq I-131, SPECT imaging
should be added to differentiate clearly thyroid beds,

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Ann Nucl Med (2014) 28:551–558

thyroid cancers and/or lymph node metastases, and OSEM3D should be applied for reconstruction of the SPECT data.

Conclusion
It is important to locate thyroid beds, extra-thyroid beds
and/or lymph node metastases after NaI-131 ablation
treatment in order to monitor the efficacy of ablation inpatients with DTC. Although HEGP is the best collimatorfor imaging I-131 ablation, MELP can be applied to not
only whole-body imaging but also SPECT imaging if
HEGP cannot be used.
Acknowledgments The author would like to thank the medical staff
of Kanazawa University Hospital. This study was partly funded by
Grants-in-Aid for Scientific Research from the Japan Society for the
Promotion of Science (22390230, 24601008, 24659558, 24791280,
24791285 and 25293260), the Society of Nuclear Medicine Technology, Japanese Society of Radiological Technology, the Nakatomi
Foundation and the Naito Foundation.
Conflict of interest

There are no conflicts of interest.

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